150 Arthropods as Simple Carriers of Disease 
that from feeding on excrement, on sputum, on open sores, or on 
putrifying matter, the flies may pass to the food or milk upon the table 
or to healthy mucous membranes, or uncontaminated wounds. 
There is nothing in its appearance to tell whether the fly that comes 
blithely to sup with you is merely unclean, or whether it has just 
finished feeding upon dejecta teeming with typhoid bacilli. 
109. Pulvillus of foot of house-fly, showing glandular hairs. 
The method of feeding of the house-fly has an important bearing 
on the question of its ability to transmit pathogenic organisms. 
Graham-Smith (1910) has shown that when feeding, flies frequently 
moisten soluble substances with “vomit” which is regurgitated from 
the crop. This is, of course, loaded with bacteria from previous 
food. When not sucked up again these drops of liquid dry, and pro¬ 
duce round marks with an opaque center and rim and an intervening 
less opaque area. Fly-specks, then, consist of both vomit spots 
and feces. Graham-Smith shows a photograph of a cupboard window 
where, on an area six inches square, there were counted eleven hundred 
and two vomit marks and nine fecal deposits. 
